<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <style>
            body{
                width: 200px;
                border: 1px solid  red;
                /*当元素的所有子元素全部浮动时(且没有高度时),自动识别高度为0
                后面的元素就会顶上来导致显示异常,
                添加1overflow:hidden解决此问题*/
                overflow: hidden;
            }
            #d1{
                width: 50px;
                height: 50px;
                background-color: pink;
                float: left;

            }
            #d2{
                width: 50px;
                height: 50px;
                background-color: green;
                float: left;

            }
            #d3{
                width: 50px;
                height: 50px;
                background-color: blue;
                float: left;

            }
        </style>
    </head>
    <body>
        <div>
            <div id="d1"></div>
            <div id="d2"></div>
            <div id="d3"></div>
        </div>
    </body>
</html>